Partitioning of calcium, magnesium, and transition metals between olivine and melt governed by the structure of the silicate melt at ambient pressure
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Bjorn Mysen
Abstract
Olivine/melt partitioning of the transition metal cations, Fe2+, Mn2+, Co2+, and Ni2+, together with Mg2+ and Ca2+, has been examined experimentally as a function of melt composition at ambient pressure. Melt structure was inferred from bulk-chemical composition, existing structural data, and 57Fe resonant absorption Mössbauer spectroscopy. Under isothermal conditions, Kolivine/meltD(i-Mg) = (Ci/CMg)olivine/(Ci/CMg)melt, is an exponential function of melt NBO/T for i = Ca2+, Mn2+, Co2+, and Ni2+. For i = Fe2+, the relationship is parabolic with maximum Kolivine/meltD(Fe2+-Mg) lt-values at NBO/T near 1. At constant melt NBO/T, Kolivine/meltD(i-Mg) increases systematically with decreasing cation radius, an effect that is more pronounced the more polymerized the melt. The Kolivine/meltD(i-Mg) melt is also a positive and linear function of Na/(Na + Ca) of Al-free melts. This latter effect results from changes in Qn-species abundance governed by Na/(Na + Ca) of the melts. The enthalpy of the exchange equilibrium, iolivine + Mgmelt = imelt + Mgolivine, derived from the temperature-dependence of Kolivine/meltD(i-Mg), is also a positive function of the ionic radius of the cation. The relationship of enthalpy to melt polymerization also depends on cation radius. The Kolivine/meltD(Fe2+-Mg) lt does not, however, follow this trend possibly because the bond distance, dFe2+-O, in the melts depends on melt composition.
The cations examined in this study are network-modifiers in silicate melts at ambient pressure. The solution behavior of network-modifying cations in melts is governed by the extent of steric hindrance near nonbridging oxygen, which in turn affects the energetics of metal-nonbridging oxygen bonds. Those structure effects, in turn, are related to the type of Qn-species, their abundance, and on the Al-distribution between the Qn-species. It is suggested, therefore, that the observed variations of mineral/melt partition coefficients with melt composition can be understood by considering bulk polymerization (NBO/T), the distribution of Al3+ among coexisting Qn-species, and the distribution of network-modifying cations among nonbridging in these Qn-species.
© 2015 by Walter de Gruyter Berlin/Boston
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- The geometric effects of VFe2+ for VMg substitution on the crystal structures of the grandidierite-ominelite series
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Articles in the same Issue
- Single-crystal FTIR and X-ray study of vishnevite, ideally [Na6(SO4)][Na2(H2O)2](Si6Al6O24)
- Crystallographic texture and microstructure of terebratulide brachiopod shell calcite: An optimized materials design with hierarchical architecture
- High-temperature phase relations and topological constraints in the quaternary system MgO-Al2O3-SiO2-Cr2O3: An experimental study
- Tilt and buckling modes, and acoustic anisotropy in layers with post-perovskite connectivity
- Optical absorption study of natural garnets of almandine-skiagite composition showing intervalence Fe2+ + Fe3+ → Fe3+ + Fe2+ charge-transfer transition
- Deriving formation constants for aqueous metal complexes from XANES spectra: Zn2+ and Fe2+ chloride complexes in hypersaline solutions
- Birnessite polytype systematics and identiÞ cation by powder X-ray diffraction
- Improved measurement of fission-track annealing in apatite using c-axis projection
- Improved modeling of fission-track annealing in apatite
- Intercalibration of FTIR and SIMS for hydrogen measurements in glasses and nominally anhydrous minerals
- Order and miscibility in the otavite–magnesite solid solution
- An infrared investigation of the otavite-magnesite solid solution
- Partitioning of calcium, magnesium, and transition metals between olivine and melt governed by the structure of the silicate melt at ambient pressure
- The geometric effects of VFe2+ for VMg substitution on the crystal structures of the grandidierite-ominelite series
- The iron oxidation state of garnet by electron microprobe: Its determination with the flank method combined with major-element analysis
- Gram-Charlier development of the atomic displacement factors into mineral structures: The case of samsonite, Ag4MnSb2S6
- Superstructure of Challis mordenite with doubled monoclinic unit cell
- Biopyribole evolution during tremolite synthesis from dolomite and quartz in CO2-H2O fluid
- The evolution of diamond morphology in the process of dissolution: Experimental data
- The pearceite-polybasite group of minerals: Crystal chemistry and new nomenclature rules
- Determination of layer stacking microstructures and intralayer transition of illite polytypes by high-resolution transmission electron microscopy (HRTEM)
- Structural behavior of Al3+ in peralkaline, metaluminous, and peraluminous silicate melts and glasses at ambient pressure
- The crystal structure of ingersonite, Ca3Mn2+Sb45+O14, and its relationships with pyrochlore
- Chemical composition, statistical analysis of the unit cell, and electrostatic modeling of the structure of Al-saturated chlorite from metamorphosed rocks
- XANES study of the oxidation state of Cr in lower mantle phases: Periclase and magnesium silicate perovskite
- Crystal chemistry of hydration in aluminous orthopyroxene
